It is previously known to use torsion rod springs as energy accumulator in operating devices for circuit-breakers. In prior art designs of this kind the springs are connected to the movable contact of the respective circuit-breaker via links or gear wheels (see e.g. German Patent No. 673 315 and U.S. Pat. No. 4,256,941). One advantage with springs of this kind is that they enable a rapid energy output since the mass of a torsion rod is concentrated near the axis of rotation, which causes the moment of inertia of the rod to become small. However, the fixed connection between the spring and the breaker contact in the prior art designs, in particular in breakers with butt contacts (i.e. contacts in which the direction of the contact movement is substantially perpendicular to the contact surface), results in a low velocity of contact separation during the first part of the contact opening phase. This renders the movement of the arc from the contact unit difficult, since a considerable amount of arcing gases containing metal vapour, etc., are generated at the contact unit before the contact gap reaches the minimum size (about 1 mm) necessary to enable a movement of the arc at all.
A further drawback in prior art designs is that the torsion spring has to be dimensioned to enable storage of relatively large energy, since the spring during the opening movement is counteracted by a contact pressure spring or some other contact pressure generating member.